Er:YAG laser ablation of tissue: effect of pulse duration and tissue type on thermal damage

Mechanical properties of perforated and partially demineralized bone grafts

Changes in flexural rigidity and compression strength of 18 sheep tibias were investigated after laser perforation and partial demineralization. Test bones were divided into three groups: Group 1, no treatment; Group 2, laser hole grid; and Group 3, laser hole grid and partial demineralization. Starting in the anterior direction at the tibial tuberosity, the flexural rigidity was determined using a nondestructive four-point bending test. The elliptical distribution of the flexural rigidity before and after a specific treatment was compared. After the bending test, a cylindrical center section of each test bone was loaded axially to failure to determine subsequent changes in compression strength. Results showed that perforation alone produced minimal reduction of rigidity and insignificant changes in compression strength. However, additional partial demineralization resulted in larger reductions. In compression testing, perforated and partially demineralized bone specimen showed marked decrease of the ultimate failure stress. The observed increase in failure strain appeared to be related to compression of the laser holes. The findings of this study suggest that partial demineralization and perforation can be applied to diaphyseal bone grafts and that their decreased mechanical properties are a function of the bone volume reductions produced by both processes.

Skin resurfacing of the face with the Erbium:YAG laser

BACKGROUND

Laser resurfacing of facial skin is a very popular method of rhytide and scar removal. Until recently, the most effective tool utilized for these purposes was the pulsed char-free carbon dioxide laser. These lasers, however, produce thermal damage related to prolonged wound healing. The Erbium (Er): YAG laser, with its 2940-nm wavelength and maximal water absorption, has been recently introduced for laser resurfacing of the facial skin.

OBJECTIVE

In this study, specific parameters for Er:YAG laser treatment of rhytides were evaluated clinically and histologically.

METHODS

Fifteen patients were treated with the Er:YAG laser. Perioral, periorbital, and total face rhytides were treated. All patients were treated with 0.8-1.0 J, 5-mm spot size, with the final fluences of 4-5 J/cm2. Patients were evaluated daily after treatment for 7 days and weekly for 2 months for erythema, healing time, improvement, and pigmentary changes. Histologic evaluation of preauricular human facial ex vivo skin was done to determine the penetration of multiple passes of Er:YAG laser in human facial skin.

RESULTS

All patients showed some degree of improvement of their rhytides. Reepithelialization occurred between 3 and 8 days. All evidence of erythema resolved between 3 and 6 weeks after treatment. The level of tissue ablation was determined to be down to: the granular layer after one pass; to the basal cell layer after two passes, to the papillary dermis after three to four passes, and deeper into the papillary and superficial reticular dermis after five to six passes.

CONCLUSION

The Er:YAG laser plays a significant role in the treatment of superficial and mid-depth rhytides.

Treatment of photoaged neck skin with the pulsed Erbium:YAG laser

BACKGROUND

The Erbium (Er):YAG laser represents a new laser approach for the treatment of rhytids and photodamaged skin. Because the Er:YAG laser's 2940-nm wavelength is at the peak of water absorption, this laser produces minimal thermal damage.

OBJECTIVE

To document the Er:YAG laser's efficacy in the treatment of neck rhytids.

METHODS

Ten patients with neck rhytids were treated with the Er:YAG laser. All individuals were evaluated for clinical improvement, scarring, and pigmentary changes.

RESULTS

All patients showed fair to excellent results with no scarring or pigmentary changes at 6 months.

CONCLUSION

The Er:YAG laser may be used to improve nonfacial photodamaged skin.

Absence of human papillomavirus DNA in the plume of erbium:YAG laser-treated warts

BACKGROUND

The erbium:YAG laser (Continuum Biomedical, Dublin, Calif.) is a new resurfacing and ablating laser that produces minimal residual thermal damage. Laser safety requires careful attention to the hazards of the laser plume. It is important to know whether viable organisms survive in the vapors. Human papillomavirus (HPV) DNA has been detected in the vapor of carbon dioxide laser-treated and electrodesiccated human warts. The presence or absence of HPV DNA in the laser plume of erbium:YAG laser-treated warts has not been previously studied to our knowledge.

OBJECTIVE

Our purpose was to determine the presence or absence of HPV DNA in the laser plume of erbium:YAG laser-treated human warts.

METHODS

One half of clinically typical and histopathologically confirmed verrucae vulgares from five patients were submitted for HPV DNA detection with in situ hybridization. After erbium:YAG laser ablation of the remainder of the warts, the laser plume was deposited on the handpiece as an abundant fluffy material and was submitted for evaluation of HPV DNA by polymerase chain reaction with consensus primers for the HPV type detected in the wart specimens.

RESULTS

HPV2 DNA was found in all warts. HPV DNA was not detected in the erbium:YAG laser plume after ablation of these same warts.

CONCLUSION

The absence of HPV DNA in the plume of erbium:YAG laser-treated warts is a significant safety feature of this laser.

Skin contraction following erbium:YAG laser resurfacing

BACKGROUND

Resurfacing the skin with deep chemical peels, dermabrasion, or lasers tightens the skin via dermal remodeling. The erbium (Er):YAG laser is a new laser for resurfacing and it removes lesional tissue efficiently with minimal residual thermal damage. In this paper, I present the first published study, to my knowledge, documenting and quantifying the cutaneous contraction following Er:YAG laser resurfacing of human skin.

OBJECTIVE

To document and measure the cutaneous contraction resulting from Er:YAG laser resurfacing.

METHODS

Using lentigos as skin markers, square areas on human forearm skin were resurfaced with the Er:YAG laser. The distance between these skin markers was measured before, immediately after, at 3 days, and weekly for 16 weeks after laser surgery.

RESULTS

After two to three passes with the Er:YAG laser, there was an immediate 4% linear tightening of the skin, which persisted at 3 days, increased to 8% at 1 weeks, was 11% at 2 and 4 weeks, 13% at 6 weeks, and 14% at 16 weeks.

CONCLUSION

Er:YAG laser resurfacing produces measurable cutaneous contraction. This phenomenon may contribute to the positive clinical tightening of human skin following Er:YAG laser resurfacing.

Improved osteoinduction of cortical bone allografts: a study of the effects of laser perforation and partial demineralization

Massive cortical bone allografts have been found to incorporate slowly into host bone and thus are subject to complications such as nonunion, fatigue fracture, and infection. To better understand and improve the process of osteoinduction in these types of bone grafts, a new experimental model was developed with use of diaphyseal cortical bone grafts from rat tibiae that were prepared by partial demineralization and drilling of 0.33 mm diameter holes with a pulsed, 2.94 microns wavelength, erbium:yttrium-aluminum-garnet laser. Six types of grafts were analyzed: untreated (Type I), demineralized 25 microns deep (Type II), demineralized 150 microns deep (Type III), laser perforated (Type V), laser perforated and then demineralized 25 microns deep (Type V), and laser perforated and then demineralized 150 microns deep (Type VI). The graft was orthotopically transplanted in the tibia of an adult Sprague-Dawley rat and followed for as long as 4 months. Histologic evaluation at 1 and 4 months postoperatively with use of hematoxylin and eosin staining confirmed that there was new bone growth in Types II, III, V, and VI grafts. The amount of growth was estimated by comparing bone mineral density before implantation with values obtained after retrieval of the graft. These measurements were correlated to histomorphometric analysis of graft incorporation. The results show that the processes of partial demineralization (p < 0.000001) and laser perforation with partial demineralization (p < 0.000001) were both significant in enhancing bone growth in this model. New bone growth was significantly increased when the grafts were prepared with extensive demineralization (p < 0.015). This study demonstrates that osteogenesis in cortical bone grafts can be fostered through the process of partial demineralization and laser perforation. To the extent that minimal partial demineralization and laser perforation allow maintenance of structural integrity while altering the osteoinductive properties in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts may be improved.

The effects of CO2, Nd:YAG and Er:YAG lasers with and without surface coolant on tooth root surfaces. An in vitro study

The objective of this study was to compare and contrast the morphologic changes in tooth root surfaces treated in vitro by scaling and root planing followed by irradiation with the Er:YAG laser using air/water surface cooling and the CO2 and Nd:YAG lasers, both with and without surface coolant. The experimental unit consisted of 42 freshly extracted teeth which were divided equally and randomly assigned to the following 7 treatment groups: untreated control, S/RP only, CO2 laser with and without air/water surface cooling, Nd:YAG laser with and without/air water surface cooling, and Er:YAG laser with air/water surface coolant. Specimens treated with CO2 laser irradiation were subjected to energy densities ranging from 100 to 400 J/cm2; those treated with the Nd:YAG from 286 to 1857 J/cm2; and the Er:YAG was used within a range of 20 to 120 J/cm2. The degree of morphologic change following CO2 and Nd:YAG irradiation appeared directly related to energy density but unrelated to the use of surface coolant. Laser induced surface changes included cavitation, globules of melted and resolidified mineral, surface crazing, and production of a superficial char layer. In contrast, the Er:YAG laser produced root surface changes that might be expected from acid etching, i.e., removal of the smear layer and exposure of the collagen matrix. In addition, sharply defined microfractures of the mineralized structure were noted and unlike the CO2 and Nd:YAG lasers, there was no evidence of melting or surface char. Given the parameters of this study, it appears that both the CO2 and Nd:YAG lasers alter the root surface in an undesirable manner. The Er:YAG laser, however, when used at low energy densities shows sufficient potential for root surface modification to warrant further investigation.

Proposal of a computerized algorithm for continuous wave CO2 laser on-line control during orthopaedic surgery. Phase II: simplified algorithm version (LCA-s) and helmet-mounted data access device solution

This paper is the continuation of the Phase I report published in 1992 by Canestri. It contains recent findings on how to speed-up the process of sublimated volume forecasting for a TEM11* CO2 laserbeam in CW mode following an original model proposed by the author--called LCA--here presented in a simplified version (LCA-s) on PMMA (polymethylmethacrilate) samples. Other interesting parameters, such as the time required to create the minimal injury vb along with its physical interpretations, are reported and explained. TEM11*, TEM01* and TEM00 beams profiles are also compared and discussed for LCA-s. The results of both Phase I and Phase II of this investigation can be integrated in one single solution package for the end-user, combining fast decisions making and operational features. The final part of this paper describes the 'helmet-mounted' data recall visor methodology which allows the surgeon to access to a data base for information retrieval during the course of an operation without interrupting the surgical case itself. This particularly interesting application allows the surgeon to consult a centrally-located data base which contains important information regarding similar clinical cases, choice of laserbeam profiles and focal lengths, simulation of beam behaviours, performances and other data. The on-line and direct access to the data base supports him in all those borderline situations in the O.R. in which the laser device type and configuration/calibration play a device role in the success of the operation. Also, the helmet-mounted display frees surgeon's hands in order to allow him to continue the operation while consulting the data base on-line, thus speeding up decision processes regarding changes of laser set-up, general calibration optimization and remote clinical consultancy.

Etch rate and spectroscopic ablation studies of Er:YAG laser-irradiated dentine

The interaction of a 200-mus Er:YAG laser at 2.94 mum with human molar dentine has been studied by ablation depth rate measurements as well as time-resolved and optical multichannel analyzer emission spectroscopy. Ablation rates indicate a threshold fluence of ~5.2 J cm(-2) for significant material removal with a low-fluence (<20 J cm(-2)) effective optical absorption coefficient of ~700 cm(-1). Deviation from a Beer's law dependence is significant in the range ~20 to ~60 J cm(-2) and indicates a maximum effective plume absorption of ~1200 cm(-1) at ~40 J cm(-2), coinciding with the appearance of strong line and broadband optical emission in the visible region. Time-of-flight emission measurements yield maximum species-resolved ablation velocities of up to ~1.2 x 10(6) cm s(-1), enabling calculation of plasma temperatures. The results suggest that etch-rate characteristics are driven by changes in plume absorption dynamics, which have a strong dependency on incident laser fluence.

Transcanalicular neodymium: YAG laser for revision of dacryocystorhinostomy

BACKGROUND

Laser-assisted dacryocystorhinostomy (DCR) has failed to match the success rates of external DCR. It has been suggested that this technology may be best suited for revision of failed DCR cases. The authors prospectively evaluated the efficacy of transcanalicular laser-assisted revision DCR (TCLARDCR).

METHODS

A neodymium:YAG (Nd:YAG) laser was used for transcanalicular revision of 24 failed DCRs. Failure had followed one (n = 15), two (n = 7), or three (n = 2) previous external DCRs.

RESULTS

Mean duration of the surgery was 78.2 minutes. Success was achieved in 11 cases (46%; mean follow-up, 20 months). There was no correlation between early loss of stents and failure. Three cases had partial relief of symptoms. Three of the failures unsuccessfully underwent further TCLARDCR.

CONCLUSIONS

The authors' success rate of 46% with TCLARDCR compares poorly with the 85% success for external revision DCR. With TCLARDCR, specific anomalies like the sump syndrome cannot be addressed adequately. There is a theoretical risk of canalicular injury. Laser lacrimal surgery also is equipment dependent and more costly than external DCR. The TCLARDCR cannot be recommended for revision DCR using the Nd:YAG laser (Lasersonics, Milpitas, CA).

Laser treatment of warts and other epidermal and dermal lesions

The CO2 laser is a versatile and effective tool for the treatment of warts and various other epidermal and dermal lesions where there is no easily targeted chromophore other than water. The development of high peak power, short-pulse, or rapidly scanned resurfacing CO2 lasers has significantly improved the safety and efficacy of using the CO2 laser. Many lesions amenable to CO2 laser vaporization can be treated by other far less expensive treatment modalities, however, and it is the laser surgeon's responsibility to use the CO2 laser only in cases in which it is demonstrably the best treatment option. The pulsed dye laser may replace the CO2 laser for the treatment of recalcitrant warts if the impressive early cure rates reported are borne out over time. Newer laser systems such as the Er:YAG laser with its extremely small zone of thermal damage may supplant the CO2 laser in the treatment of other epidermal and dermal lesions in the future.

Ab interno infrared laser trabecular ablation: preliminary short-term results in patients with open-angle glaucoma

BACKGROUND

Outflow obstruction of trabecular drainage structures results in elevation of intraocular pressure (IOP) in various forms of chronic open-angle glaucoma. In vitro studies have shown that laser trabecular ablation (LTA) with opening of Schlemm's canal can be reproducibly performed by use of infrared lasers with minimal damage to collateral tissue structures.

METHODS

In order to investigate the clinical applicability and efficacy of ab interno contact laser photoablation of trabecular meshwork in the surgical treatment of human glaucoma, we conducted a pilot study using an erbium: YAG laser (2.94 microns) with a quartz fiber endoprobe (320 microns core diameter) applying 10-20 single laser pulses (5-7 mJ) to the trabecular meshwork.

RESULTS

Under goniocopic visualization trabecular tissue was photovaporized in eight patients with primary or secondary chronic open-angle glaucoma. Intraoperatively, moderate reflux bleeding occurred from laser-induced craters. No major intra- or postoperative complications occurred. Preoperative and postoperative gonioscopy of the treated area demonstrated successful removal of trabecular tissue. Mean IOP was reduced from 36.1 mmHg ot 21.3 mmHg at a limited follow-up of 3 months.

CONCLUSION

With modifications this technique may have clinical potential in the surgical management of glaucoma. Prospective long-term studies with more patients are warranted to evaluate the outcome of LTA.

Photovaporization rate and profile of an erbium-chromium:YAG laser in the fundamental mode

PURPOSE

To evaluate the ablation characteristics of an experimental erbium:YAG (Er:YAG) laser and assess whether it delivers sufficient output for performing photorefractive keratectomy.

SETTING

Department of Ophthalmology, Virchow-Clinics, Humboldt University, Berlin, Germany.

METHODS

An experimental Er:YAG laser, the erbium-chromium:YAG, running in fundamental mode was used to evaluate the energy profile. Measurements obtained using a joulemeter were compared to the ablation profiles of cadaver pig eyes. The pig eyes were treated with different fluences (mean 0.8 to 2.9 J/cm2) and, after histological preparation, were examined using light and scanning electron microscopy.

RESULTS

Measurements with the joulemeter and in the cadaver pig eyes showed a Gaussian-curved profile of energy (ablation). In the current setting, the diameter of ablation was 3.5 mm. Histological examination showed a homogeneous profile of ablation with minor thermal damage.

CONCLUSION

The Er:YAG laser running in the fundamental mode allows homogeneous ablation of corneal tissue. The Er:YAG laser is easier to handle technically than the excimer laser and has none of the potential risks of ultraviolet light.

Morphological changes elicited in skeletal muscle by a Nd:YAG laser scalpel and electrocautery during surgical reduction of the human tongue

A Nd:YAG laser scalpel was used for the surgical reduction of a human hyperplastic tongue. This instrument combines a fine cutting precision with haemostatic properties, whereby loss of blood is minimized and the surgeon's field of view unimpeded by flooding from the damaged capillary bed. The coagulative properties of Nd:YAG laser light are, however, insufficient to effect blood flow stasis in larger calibre vessels (arteries > 2 mm; veins > 3-5 mm), such as those located at the base of the tongue. For this purpose, bipolar diathermy (electrocautery) was employed. The ultrastructural changes incurred by skeletal muscle fibres using these two "heat" sources were compared. The damage profile elicited using each modality was similar: coagulation of myofilamentous proteins leads to destruction of fibrillar architecture with concomitant loss of periodic banding; on moving away from the wound margin, characteristic features are gradually restored. As the severity of these heat-induced effects decreases, there is a corresponding increase in superimposed dislocation and tearing phenomena induced by post-treatment swelling.

The effect of pulpotomy using CO2 and Nd:YAG lasers on dental pulp tissue

The histological response of the dental pulp after laser irradiation was studied. After pulpotomy was performed in the premolar and molar teeth of dogs, the exposed pulp tissue at the root canal opening was lased using either a CO2 or Nd:YAG laser. The laser parameters were 2 W, 10 ms, 5 times per second for 1, 2 and 3 s for CO2 laser and 2 W, 20 pulses per second for 1, 2 and 3 s for the Nd:YAG laser. Observations were made 30 and 45 days after treatment. The results revealed that laser irradiation caused carbonization, necrosis, infiltration of inflammation cells, oedema and haemorrhage in the pulp tissue. Under the conditions of this experiment, there was little histological evidence of repair to the treated pulp with a newly formed dentine barrier, which was in contrast to the control samples treated with a calcium hydroxide-containing cement (Dycal).

Histologic analysis of thermal effects of laser thermokeratoplasty and corneal ablation using Sirius-red polarization microscopy

PURPOSE

To evaluate how well several histologic techniques differentiate degrees of thermally induced changes in corneal tissue after laser thermokeratoplasty (LTK) or corneal ablation.

SETTING

Medical Laser Center Lübeck, Germany.

METHODS

Corneas of freshly enucleated porcine eyes were treated with a continuous wave laser diode (1.86 microns) and a pulsed chromium-thulium-holmium: YAG laser (2.1 microns) to produce LTK lesions or ablated with a Q-switched and a free-running chromium-erbium: YSGG laser (2.70 microns), a free-running erbium: YAG laser (2.94 microns), and an argon-fluoride excimer laser (193 nm). The lesions were evaluated by light microscopy (LM) (hematoxylin and eosin, Azan, van Gieson's, and Masson-Goldner's trichrome stains), transmission electron microscopy (TEM), and polarization microscopy after Sirius-red staining. Sirius-red, a strongly elongated, birefringent molecule binding parallel to collagen molecules, was used to enhance corneal birefringence.

RESULTS

With routine LM, it was difficult to discriminate the degrees of thermal alterations in LTK lesions. Combined Sirius-red staining and polarization microscopy distinguished between a strongly coagulated central zone and the transition zone to normal tissue. Sirius-red uptake was increased in both zones, reflecting the availability of new binding sites. The central zone appeared darker under polarization than normal collagen because of a loss of birefringence. Intrinsic birefringence was greatly reduced; however, form birefringence partly remained as long as some collagen fibrils were intact. In the center of very strong lesions, where the collagen was hyalinized, birefringence was completely lost because of the complete disintegration of the fibrillar structure, which was visible under TEM. The transition zone toward normal cornea showed increased birefringence because the natural birefringence was largely preserved and enhanced by the increased Sirius-red uptake. Mechanical stretching between neighboring LTK lesions was manifested by increased birefringence.

CONCLUSION

Sirius red offered an improved and simple histologic method for analyzing thermal collagen changes. It may contribute to a better understanding of the working mechanisms of LTK and improve analysis of thermal effects in corneal ablation.

Prospective study of ab externo erbium:YAG laser sclerostomy in humans

PURPOSE

To evaluate the efficacy of ab externo erbium:YAG (Er:YAG) laser sclerostomy in controlling intraocular pressure in eyes with uncontrolled glaucoma.

METHODS

We performed ab externo laser sclerostomy on eyes of 26 patients. Mean +/- SD postoperative follow-up was 11.4 +/- 0.9 months. Complete success was defined as intraocular pressure below 22 mm Hg with no adjunct medication; qualified success was defined as intraocular pressure below 22 mm Hg with medication.

RESULTS

In all eyes, ab externo Er:YAG laser sclerostomy achieved a functioning fistula with a prominent filtering bleb. Twelve eyes had had neodymium:YAG (Nd:YAG) laser iridotomy at the site of laser sclerostomy 2 weeks before filtering surgery; 14 eyes had surgical iridectomy at the site of laser sclerostomy. Mean preoperative intraocular pressure of 30.7 +/- 7.3 mm Hg (range, 17.0 to 48.0 mm Hg) was significantly (P < .05) reduced to 18.3 +/- 1.0 mm Hg (range, 0 to 25.0 mm Hg) at 2 weeks postoperatively. thereafter, marked regression was noted: at 1 month postoperatively, intraocular pressure was 20.1 +/- 9.5 mm Hg (range, 4.0 to 44.0 mm Hg); half-life of complete success was 25 days; of qualified success, 56 days; and of a functioning filtering bleb, 36 days.

CONCLUSIONS

Ab externo Er:YAG laser sclerostomy reliably created successful full-thickness fistulae with prominent filtering blebs in human glaucomatous eyes. However, a transient phase of ocular hypotony caused by aqueous overfiltration, followed by an ongoing rate of fistula patency failure, renders Er:YAG laser sclerostomy, as performed in this study, unsuitable for long-term pressure control.

Multicenter clinical experience using an erbium:YAG laser for vitreoretinal surgery

PURPOSE

To evaluate the advantages, disadvantages, safety, complications, and surgical applicability of an erbium:YAG laser system for maneuvers in vitreoretinal surgery.

METHODS

A prospective, consecutive trial of 68 eyes in 66 patients undergoing vitreoretinal surgery in which an erbium:YAG laser with graduated output from 0.2 to 5.0 mJ per pulse, repetition rate of 2 to 30 Hz, and equipped with a flexible fiber optic and interchangeable 20-gauge intraocular fiber optic endoprobes was used to perform specific maneuvers, including transection, incision, and ablation of membranes, retinotomy, vessel coagulation, iridectomy, and lens tissue ablation. The patients were treated in five centers in contemporary vitreoretinal surgical settings for surgical indications, including proliferative diabetic retinopathy, proliferative vitreoretinopathy, epiretinal membrane, and retinopathy of prematurity.

RESULTS

One hundred seventy-four maneuvers were performed with an overall surgical efficacy rating of excellent or good in 84% of maneuvers, ranging from a high of 100% for subretinal membrane transection to a low of 25% for coagulation of blood vessels. Complications included retinal break or photocoagulative injury in 5% of epiretinal membrane incisions, minor bleeding from transected retinal vessels during 29% of retinotomies, and intraocular lens damage during two posterior capsulotomies. The most significant limitation was the cautious pace used during maneuvers near the retinal surface.

CONCLUSION

The erbium:YAG laser is capable of versatile new approaches offering precise tissue cutting and ablation in vitreoretinal surgical maneuvers with a high degree of safety. The main limitation encountered was the slow speed of certain critical maneuvers near the retina.

Laser skin resurfacing

There has always been interest in looking younger, but recently there seems to have been an explosion of public interest in facial rejuvenation. Physicians have been treating photodamaged skin for many years by removing the epidermis and a variable thickness of dermis with dermabrasion or chemical peels, with the expectation that reepithialization and collagen remodeling will result in a more youthful appearance. With the recent development of short-pulsed high-peak power and rapidly scanned carbon dioxide (CO2) lasers, the ability to remove photodamaged skin in a precise and reproducible manner while leaving behind a narrow zone of thermal damage has been achieved. This development has generated tremendous interest in laser skin resurfacing as a technique to reverse photoaging.

Combination of fiber-guided pulsed erbium and holmium laser radiation for tissue ablation under water

Because of the high absorption of near-infrared laser radiation in biological tissue, erbium lasers and holmium lasers emitting at 3 and 2 µm, respectively, have been proven to have optimal qualities for cutting or welding and coagulating tissue. To combine the advantages of both wavelengths, we realized a multiwavelength laser system by simultaneously guiding erbium and holmium laser radiation by means of a single zirconium fluoride (ZrF(4)) fiber. Laser-induced channel formation in water and poly(acrylamide) gel was investigated by the use of a time-resolved flash-photography setup, while pressure transients were recorded simultaneously with a needle hydrophone. The shapes and depths of vapor channels produced in water and in a submerged gel after single erbium and after combination erbium-holmium radiation delivered by means of a 400-µm ZrF(4) fiber were measured. Transmission measurements were performed to determine the amount of pulse energy available for tissue ablation. The effects of laser wavelength and the delay time between pulses of different wavelengths on the photomechanical and photothermal responses of meniscal tissue were evaluated in vitro by the use of histology. It was observed that the use of a short (200-µs, 100-mJ) holmium laser pulse as a prepulse to generate a vapor bubble through which the ablating erbium laser pulse can be transmitted (delay time, 100 µs) increases the cutting depth in meniscus from 450 to 1120 µm as compared with the depth following a single erbium pulse. The results indicate that a combination of erbium and holmium laser radiation precisely and efficiently cuts tissue under water with 20-50-µm collateral tissue damage.

Thermodynamic response of soft biological tissues to pulsed infrared-laser irradiation

The physical mechanisms that achieve tissue removal through the delivery of short pulses of high-intensity infrared laser radiation, in a process known as laser ablation, remain obscure. The thermodynamic response of biological tissue to pulsed infrared laser irradiation was investigated by measuring and analyzing the stress transients generated by Q-sw Er:YSGG (lambda = 2.79 microns) and TEA CO2 (lambda = 10.6 microns) laser irradiation of porcine dermis using thin-film piezoelectric transducers. For radiant exposures that do not produce material removal, the stress transients are consistent with thermal expansion of the tissue samples. The temporal structure of the stress transients generated at the threshold radiant exposure for ablation indicates that the onset of material removal is delayed with respect to irradiation. Once material removal is achieved, the magnitude of the peak compressive stress and its variation with radiant exposure are consistent with a model that considers this process as an explosive event occurring after the laser pulse. This mechanism is different from ArF- and KrF-excimer laser ablation where absorption of ultraviolet radiation by the collagenous tissue matrix leads to tissue decomposition during irradiation and results in material removal via rapid surface vaporization. It appears that under the conditions examined in this study, explosive boiling of tissue water is the process that mediates the ablation event. This study provides evidence that the dynamics and mechanism of tissue ablation processes can be altered by targeting tissue water rather than the tissue structural matrix.

Temperature measurements during phacoemulsification and erbium:YAG laser phacoablation in model systems

PURPOSE

To compare the potential for thermal injury to ocular structure resulting from phacoemulsification ultrasound energy and erbium:YAG (Er:YAG) laser output.

SETTING

Morse Laser Laboratory, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston.

METHODS

Ultrasonic phacoemulsification energy and ER:YAG laser output (10 J/cm2, 10 Hz, 0.3 watts) sufficient for lens removal were applied to model systems and human cadaver eyes. Temperatures were measured with ultrafine thermocouples interfaced to a microcomputer data acquisition system.

RESULTS

Although greater than 95% of energy from laser output is converted to thermal energy, temperature rise in model systems and cadaver eyes was 10 to 15 times greater after pulsed application of ultrasound energy than after Er:YAG laser application. At 100% power, approximately 4 watts of ultrasound power is converted to heat. Temperature rise following both laser and ultrasound applications decreased with irrigation in cadaver eyes and increasing volume in a model system. With continuous irrigation (20 cc/min), the temperature rise at 2 minutes measured at the corneal endothelial surface, within the corneal stroma, and in the anterior chamber angle of cadaver eyes was approximately 0.5 degrees Celsius (degrees C) after laser application and 7.0 degrees C after ultrasound application. Without irrigation, temperatures rose 2.5 degrees C after laser application and 35.0 degrees C after ultrasound application.

CONCLUSION

At operating parameters sufficient for lens removal, the Er:YAG laser imparted less thermal energy to whole eyes and model systems than ultrasonic phacoemulsification.

Initial clinical experience with an erbium:YAG laser for vitreoretinal surgery

PURPOSE

We tested the efficacy of an erbium:YAG laser for maneuvers in patients undergoing vitreoretinal surgery.

METHODS

An erbium:YAG laser equipped with a flexible fiberoptic and interchangeable 20-gauge endoprobes of various tip configurations ranging from 100 to 365 microns was used for specific maneuvers in 13 patients referred for vitreoretinal surgery for diabetic traction detachment, proliferative vitreoretinopathy, retinal detachment with posterior break, and epimacular membrane. The following maneuvers were performed: (1) transection of elevated vitreous membranes, (2) incision of epiretinal membranes, (3) drainage and relaxing retinotomy, (4) transection of subretinal membranes, (5) noncontact ablation of epiretinal membranes in air-filled eyes, (6) ablation of lens remnants, (7) posterior capsulotomy, (8) iris surgery, and (9) retinal vascular coagulation.

RESULTS

Forty-eight defined maneuvers were performed with energy levels ranging from 0.2 to 5.0 mJ and repetition rates of 2 to 30 Hz. Transection of elevated membranes, subretinal membranes, and retinotomies were easily performed. Fourteen incisions into vascularized epiretinal membranes in diabetic traction detachment surgery demonstrated a fine margin of coagulation that permitted hemostatic incision. Retinal breaks were created during one of these incisions. Lens remnant ablation, posterior capsulotomy, and iris tissue removal were successful, with a single complication consisting of damage to the posterior surface of an intraocular lens during a pars plana posterior capsulotomy accomplished by means of a side-firing probe. Epiretinal membrane ablations in air-filled eyes were effectively performed in a gradual fashion without hemorrhage.

CONCLUSIONS

The erbium:YAG laser offers precise and effective tissue cutting and removal in vitreoretinal maneuvers. Further study will determine the role of this technology in vitreoretinal surgery.

Erbium laser ablation of dental hard tissue: effect of water cooling

BACKGROUND AND OBJECTIVE

Several lasers have been explored for hard dental tissue applications; used alone they have resulted in potentially harmful temperature increases in the pulp chamber.

MATERIALS AND METHODS

An Er:YAG laser (lambda = 2.94 microns) was used to ablate hard dental tissues. Ablation rates with and without a water-cooling spray were measured. Subsequent experiments investigated the cooling effects of the water. Initially single channels were drilled into dentin; further studies involved ablating rectangular areas with repetition rates up to 10 Hz.

RESULTS

The water spray minimally reduced the ablation rates of dentin and did not affect the ablation rates of enamel. The water spray effectively cooled the teeth; while using the maximum average power investigated (10 Hz, 360 mJ/pulse), a water flow rate of 4.5 ml/min limited the temperature rise in the pulp chamber to less than 3 degrees C.

CONCLUSION

The studies confirm the feasibility of using an Er:YAG laser in conjunction with a water spray to safely and effectively remove hard dental tissues.

Erbium laser ablation of dental hard tissue: effect of water cooling

BACKGROUND AND OBJECTIVE

Several lasers have been explored for hard dental tissue applications; used alone they have resulted in potentially harmful temperature increases in the pulp chamber.

MATERIALS AND METHODS

An Er:YAG laser (lambda = 2.94 microns) was used to ablate hard dental tissues. Ablation rates with and without a water-cooling spray were measured. Subsequent experiments investigated the cooling effects of the water. Initially single channels were drilled into dentin; further studies involved ablating rectangular areas with repetition rates up to 10 Hz.

RESULTS

The water spray minimally reduced the ablation rates of dentin and did not affect the ablation rates of enamel. The water spray effectively cooled the teeth; while using the maximum average power investigated (10 Hz, 360 mJ/pulse), a water flow rate of 4.5 ml/min limited the temperature rise in the pulp chamber to less than 3 degrees C.

CONCLUSION

The studies confirm the feasibility of using an Er:YAG laser in conjunction with a water spray to safely and effectively remove hard dental tissues.

Effect of Er:YAG laser holes on osteoinduction in demineralized rat calvarial allografts

Massive cortical autografts and allografts have been found to incorporate into host bone very slowly and thus are subject to complications such as fatigue fracture and infection. In order to understand and improve the process of osteogenesis in these types of bone grafts, a new experimental model was developed using bone discs from rat calvaria prepared by demineralization and drilling of 0.5 mm diameter holes with a pulsed, 2.94 microns wavelength Erbium:Yttrium-Aluminum-Garnet laser. Four types of bone discs were analyzed: untreated (Type I), demineralized (Type II), laser-ablated (Type III), and laser-ablated then demineralized (Type IV). The discs were transplanted into a subcutaneous site in adult Sprague-Dawley rats and followed for as long as 6 weeks. Histologic analysis of the discs at weekly intervals with use of hematoxylin and eosin staining confirmed the presence of new bone growth in Type-II and Type-IV discs. The amount of new bone growth in each disc was estimated by determining the mineral x-ray attenuation coefficient, which is proportional to mineral density, from digitized radiographs of the discs. The results showed that the processes of demineralization (P < 0.001) and laser ablation with demineralization (p < 0.05) were both significant in enhancing new bone growth in this model. This study demonstrated that osteoinduction can be fostered in cortical bone through the processes of demineralization and laser ablation. To the extent that laser ablation may allow maintenance of structural integrity while altering the surface geometry in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts might be improved.

Bactericidal effect of erbium YAG laser on periodontopathic bacteria

BACKGROUND AND OBJECTIVE

Recently Erbium (Er) YAG laser has been developed for dentistry. It may be suitable for periodontal therapy. This study examined the bactericidal effect of the Er: YAG laser on periodontopathic bacteria in vitro.

STUDY DESIGN/MATERIALS AND METHODS

After spreading the bacterial suspension of Porphyromonas gingivalis or Actinobacillus actinomycetemcomitans on agar plates, a single pulse laser was applied to the agar plates at the energy density of 0.04-2.6 J/cm2. The growth of the bacterial colonies on the lased agar plates was examined after anaerobic culture. P. gingivalis colonies were also individually exposed to the single pulse laser at the energy of 1.8-10.6 J/cm2. The colony forming units of the irradiated colonies were counted.

RESULTS

Growth inhibitory zones were found at the irradiated sites at the energy of about 0.3 J/cm2 and higher. The survival ratios of the viable bacteria in the lased P. gingivalis colonies decreased significantly at the energy of 7.1 and 10.6 J/cm2, as compared with that of the control.

CONCLUSION

These findings suggest that the Er:YAG laser has a high bactericidal potential at a low energy level.

Use of the Er:YAG laser for improved plating in maxillofacial surgery: comparison of bone healing in laser and drill osteotomies

BACKGROUND AND OBJECTIVE

Surgical reconstruction of bony defects in the maxillofacial region involves fixation of bony fragments with mini and micro plates. Bone stabilization during hole drilling is often challenging due to the need to apply pressure when using a conventional mechanical Hall drill. In addition, fragmentation of the fragile bones may occur and complicate the reconstruction. The pulsed Er:YAG laser offers an attractive alternative drilling modality because it does not require physical contact with the bone in order to drill holes, cuts bone with minimal thermal damage, and allows precise control of bone cutting. The objective of this study was to investigate the pulsed Er:YAG laser as an alternative to the mechanical bur by comparing bone healing using both modalities.

STUDY DESIGN/MATERIALS AND METHODS

Bone healing in an inferior border defect of the rat mandible was examined using either an Er:YAG laser or a mechanical bur for drilling. The healing of osteotomies in facial bones and of screw holes for plate stabilization of free bone fragments was studied.

RESULTS

All defects healed by 4 weeks postoperatively. Histologic evaluation demonstrated no difference in the amount of newly formed woven bone at the osteotomy site or screw holes made by either the laser or the drill. The extent of thermal damage at the osteotomy sites was comparable in laser and mechanically cut bone fragments.

CONCLUSIONS

On the basis of this study we suggest that the Er: YAG laser can be used clinically in thin, fragile bones in the maxillofacial region.

Repopulation of laser-perforated chondroepiphyseal matrix with xenogeneic chondrocytes. An experimental model

Growth of chondrocytes into a xenogeneic chondroepiphyseal matrix was investigated in an in vitro experimental model by combining viable calf chondrocytes with chick epiphyseal matrix devoid of viable chondrocytes. The chondrocytes were harvested from the wrist joints of newborn calves and cultured for 2 days. The epiphyses were harvested from the distal femurs and the proximal tibias of fetal chicks after development was arrested at 17 days by freezing. The epiphyseal specimens were prepared in four ways. These included femoral and tibial epiphyses without holes and femoral and tibial epiphyses with holes made by a laser. These epiphyseal specimens were co-cultured with calf chondrocytes for various periods. After digestion of the epiphyseal matrix, viable chondrocytes were counted in suspension. Chondrocyte division in the matrix was assessed by [3H]thymidine incorporation. The growth of calf chondrocytes into the xenogeneic chick matrix was evaluated by fluorescence microscopy on fresh thick epiphyseal sections. The percentage of viable chondrocytes in the xenogeneic epiphyseal matrix increased with culture time to a maximum at day 21. The addition of laser-drilled holes was found to extend a plateau of chondrocyte viability until day 29. A decrease in cell viability was detected at later observation points. This study demonstrates that xenogeneic matrix may serve as a morphogenetic scaffold for chondrocytic growth.

Study of photoablation of rabbit corneas by Er:YAG laser

BACKGROUND AND OBJECTIVE

This work studied the ablation mechanisms of rabbit corneas by the Erbium:YAG laser. The occurrence of thermal and mechanical damages in the tissue as a function of the laser fluence was also investigated.

STUDY DESIGN/MATERIALS AND METHODS

The experiments were performed both on enucleated eyes and in vivo. An ultrafast imaging technique was used to investigate the dynamic evolution of the ablation. The treated samples underwent histological and ultrastructural study.

RESULTS

A single high fluence laser shot led to the complete removal of the epithelium by a photomechanical effect. In eyes whose epithelium was manually removed, high fluence pulses resulted in evident tears in the stroma, whereas low fluence pulses led to few microns deep incisions, characterized by limited mechanical and thermal damages.

CONCLUSION

The photomechanical action plays a significant role in the ablation of the cornea by Erbium laser. Precise control of the fluence is required to avoid cracking phenomena in the stroma.

New semiconductor laser for vitreoretinal surgery

BACKGROUND AND OBJECTIVE

We investigated the potential application in vitreoretinal surgery of a CW diode laser with cutting capabilities.

STUDY DESIGN/MATERIALS AND METHODS

A semiconductor CW laser emitting 300 mW optical power at 1.94 microns wavelength was used to perform retinotomies and membrane cutting on rabbit eyes. The device was integrated into a dedicated controller. The laser radiation was delivered through a low attenuation fused silica optical fiber of 200 microns core size, terminating into a 20-gauge endo-ocular handpiece. Histological aspects of threshold lesions obtained on the rabbits' chorioretina were evaluated by light microscopy.

RESULTS

We obtained circular and linear full-thickness retinotomies with contact and noncontact procedures using energy of 120 mJ (240 mW x 0.5 s). Using a non-contact procedure, a larger peripheral coagulation halo around the retinotomies was observed, as compared to the contact method. The adjacent zone of thermal damage ranged from 50 to 200 microns. Lower efficacy was obtained on experimentally induced epiretinal membranes, where only superficial ablation was achieved.

CONCLUSION

The CW 2 microns diode laser will have a promising future in vitreoretinal surgery when a higher output irradiance is available.

Pulsed Erbium:YAG laser ablation in cutaneous surgery

BACKGROUND AND OBJECTIVE

Among the various pulsed midinfrared-lasers studied in skin surgery the 2.94 microns Erbium:YAG laser has been shown to combine most efficacious ablation with least thermal damage due to its unique absorption characteristics in tissue water. A newly developed high-power Erbium:YAG laboratory laser providing output energies (up to 1.5 J/pulse) and repetition rates (up to 15 Hz) appropriate for clinical use enabled us to investigate its potential indications in dermatological surgery.

STUDY DESIGN/MATERIALS AND METHODS

Erbium:YAG laser ablation was performed in vitro on pig skin and in vivo on a total of 30 patients presenting with different skin disorders.

RESULTS

In vitro ablation efficiency linearly increased with radiant exposure and was inversely correlated with pulse frequency. Ablation rate at 10 Jcm-2 (used clinically) measured from approximately 10 microns (at 10 Hz) to 40 microns (at 1 Hz). Also for high repetition rates thermal necrosis did not exceed 50 microns, corresponding clinically to capillary bleeding after exposure of the dermis. Superficial lesions, such as epidermal nevi, were easily ablated and re-epithelization was unimpaired owing to the absence of tissue necrosis. In tattoos, exposed pigment particles were precisely removed. However, in deeper lesions the casual onset of bleeding impeded the procedure and scar formation was observed after reepithelization.

CONCLUSION

Pulsed 2.94 microns Erbium:YAG laser surgery allows an extremely precise etching of delicate superficial skin lesions and also should have a potential for skin resurfacing.

The thermodynamic response of soft biological tissues to pulsed ultraviolet laser irradiation

The physical mechanisms that enable short pulses of high-intensity ultraviolet laser radiation to remove tissue, in a process known as laser ablation, remain obscure. The thermodynamic response of biological tissue to pulsed laser irradiation was investigated by measuring and subsequently analyzing the stress transients generated by pulsed argon fluorine (ArF, lambda = 193 nm) and krypton fluorine (KrF, lambda = 248 nm) excimer laser irradiation of porcine dermis using thin-film piezoelectric transducers. For radiant exposures that do not cause material removal, the stress transients are consistent with rapid thermal expansion of the tissue. At the threshold radiant exposure for ablation, the peak stress amplitude generated by 248 nm irradiation is more than an order of magnitude larger than that produced by 193 nm irradiation. For radiant exposures where material removal is achieved, the temporal structure of the stress transient indicates that the onset of material removal occurs during irradiation. In this regime, the variation of the peak compressive stress with radiant exposure is consistent with laser-induced rapid surface vaporization. For 193 nm irradiation, ionization of the ablated material occurs at even greater radiant exposures and is accompanied by a change in the variation of peak stress with radiant exposure consistent with a plasma-mediated ablation process. These results suggest that absorption of ultraviolet laser radiation by the extracellular matrix of tissue leads to decomposition of tissue on the time scale of the laser pulse. The difference in volumetric energy density at ablation threshold between the two wavelengths indicates that the larger stresses generated by 248 nm irradiation may facilitate the onset of material removal. However, once material removal is achieved, the stress measurements demonstrate that energy not directly responsible for target decomposition contributes to increasing the specific energy of the plume (and plasma, when present), which drives the gas dynamic expansion of ablated material. This provides direct evidence that ultraviolet laser ablation of soft biological tissues is a surface-mediated process and not explosive in nature.

Thermal Collateral Damage in Porcine Corneas After Photoablation With Free Electron Laser

BACKGROUND

The study describes a quantitative and systematic investigation of the collateral thermal damage during infrared photoablation as a function of wavelength between 2.7 and 6.7 microns.

METHODS

Using the tunable Free Electron Laser at Vanderbilt University, Nashville, Tenn, 60 freshly removed porcine cadaver eyes were irradiated at wavelengths between 2.7 and 6.7 microns, at a fluence of 1.3 J/cm2. For wavelengths where no photoablation occurred, fluence was increased to 3.5 J/cm2; pulse length (macropulse) was 4 microseconds, consisting of a train of micropulses (pulse duration 2 ps at a 2.9 GHz repetition rate). The corneal buttons were removed and stained with hematoxylin and eosin (H&E) and analyzed by histologic micrometry.

RESULTS

Two thermal damage zones in the remaining tissue were observed: zone 1 showed superficial carbonization and measured between 2 and 4 microns; beyond, the eosinophilic zone 2 measured between 10 and 100 microns. The extent of zone 2 was inversely related to the absorption spectra of the cornea; it was minimal at the 3- and 6-micrometer water absorption bands and maximal at minimal target absorption.

CONCLUSION

The results correlated well with a model of the ablation process. The study provides a systematic and predictive element for the determination of collateral thermal adverse effects; it does not yet include pulse length variation as a determining factor.

Erbium:YAG laser surgery of the vitreous and retina

PURPOSE

These studies evaluated an erbium:YAG laser for transection of vitreous membranes, retinotomy, and incision and ablation of epiretinal membranes.

METHODS

Elevated vitreous membranes, detachments, and epiretinal membranes were induced in rabbit eyes. An erbium:YAG laser, emitting at a wavelength of 2.94 microns and equipped with a flexible fiber and endoprobes with tips ranging from 75 to 375 microns, was used to perform vitreous membrane transections, retinotomies, and epiretinal membrane incisions and ablations in nontransmitting aqueous media with the endoprobe in proximity to the tissue. Ablations of epiretinal membranes also were performed in transmitting media, including air and perfluoro-N-octane with the endoprobe elevated above the membrane.

RESULTS

Twenty-five vitreous membrane transections were made in 16 eyes at distances ranging from 0.5 to 4.5 mm from the retina with radiant exposures ranging from 2 to 50 J/cm2 with nonhemorrhagic retinal damage in a single transection. Sharp, linear retinotomies were created successfully in five eyes. Epiretinal membrane ablations were performed with radiant exposures ranging from 1.8 to 22.6 J/cm2. In aqueous media, results of microscopic examination showed partial- to full-thickness ablation with a maximum lateral thermal damage of 50 microns. In air- and perfluoro-N-octane-filled eyes, there was increased lateral damage with desiccation of residual tissue. In 12 aqueous-filled eyes, 18 linear incisions were successfully performed, with retinal nonhemorrhagic damage in 2 eyes and hemorrhage in 5.

CONCLUSION

The erbium:YAG laser may provide new approaches to maneuvers performed in vitreoretinal surgery.

In vitro studies on laser scaling of subgingival calculus with an erbium:YAG laser

The effectiveness of a newly-developed Er:YAG laser with a fiber delivery system to remove subgingival calculus was examined in vitro. Fifty-three (53) periodontally-involved human extracted teeth with a band of subgingival calculus were used. Two experiments were conducted: in experiment 1, laser scaling was performed with water irrigation on a straight line and on a broad area, against the subgingival calculus at the energy levels of 10 to 120 mJ/pulse (3.5 to 42.4 J/cm2/pulse) and the pulse repetition rate of 10 pps. The morphological changes of the laser-scaled site were observed by SEM, and the efficiency of laser scaling was determined. In experiment 2, laser scaling was performed with and without water irrigation at 30 mJ/pulse and 10 pps. The morphological changes, the efficiencies, and temperature changes with and without water irrigation were compared. The pulsed Er:YAG laser used with water irrigation was able to remove the subgingival calculus from the tooth root effectively at the energy level of about 30 mJ/pulse (energy density: 10.6 J/cm2/pulse) and 10 pps, under in vitro conditions. Ablation of the tooth substance on laser scaling was generally observed within the cementum. There was little increase in temperature on the root surface during laser scaling. This study suggests the potential for the clinical application of the Er:YAG laser in subgingival scaling.

Tissue ablation by a free-electron laser tuned to the amide II band

Efforts to ablate soft tissue with conventional lasers have been limited by collateral damage and by concern over potential photochemical effects. Motivated by the thermal-confinement model, past infrared investigations targeted the OH-stretch mode of water with fast pulses from lasers emitting near 3,000 nm (refs 1, 7-9). What does a free-electron laser offer for the investigation of tissue ablation? Operating at non-photochemical single-photon energies, these infrared sources can produce trains of picosecond pulses tunable to the vibrational modes of proteins, lipids and/or water. We report here that targeting free-electron laser radiation to the amide II band of proteins leads to tissue ablation characterized by minimal collateral damage while maintaining a substantial ablation rate. To account for these observations we propose a novel ablation mechanism based on compromising tissue through resonant denaturation of structural proteins.

Erbium:YAG laser photothermal retinal ablation in enucleated rabbit eyes

The erbium:YAG laser has been shown to produce precise tissue ablation because of the high water absorption of the 2.94-microns wave-length emitted by this laser. We used an experimental system to create lesions of various depths in the surface of the rabbit retina in enucleated eyes in vitro to examine the potential application to maneuvers such as retinotomy and the removal of epiretinal membranes in vitrectomy. With an air/retinal interface, single pulses produced discrete craters in the retinal surface with a depth proportional to fluence, ranging from 30 microns for a pulse of 1.3 J/cm2 to a full-thickness retinotomy at 3.9 J/cm2. An adjacent zone of coagulated tissue ranging in size from 15 to 40 microns was noted. Multiple pulses had an additive effect. With a fluid/retinal interface, 20 pulses of 3.6 J/cm2 produced a full-thickness retinotomy, with an adjacent zone of damaged tissue up to 1 mm, caused by effects of volatilization of intervening fluid. The erbium:YAG laser may have a role in vitreoretinal surgery.

Cutting and skin-ablative properties of pulsed mid-infrared laser surgery

BACKGROUND

Pulsed mid-infrared lasers allow a precise removal of soft tissues with only minimal thermal damage.

OBJECTIVE

To study the potential dermatosurgical usefulness of currently available systems at different wavelengths (2010-nm Thulium:YAG laser, 2100-nm Holmium:YAG laser, 2790-nm Erbium:YSGG laser, and 2940-nm Erbium:YAG laser) in vivo on pig skin.

METHODS

Immediate effects and wound healing of superficial laser-abrasions and incisions were compared with those of identical control lesions produced by dermabrasion, scalpel incisions, or laser surgery performed by a 1060-nm Nd:YAG and a 1060-nm CO2 laser (continuous and superpulsed mode).

RESULTS

Best efficiency and least thermal injury was found for the pulsed Erbium:YAG laser, leading to ablative and incisional lesions comparable to those obtained by dermabrasion or superficial scalpel incisions, respectively.

CONCLUSION

In contrast to other mid-infrared lasers tested, the 2940-nm Erbium:YAG laser thus provides a potential instrument for future applications in skin surgery, especially when aiming at a careful ablative removal of delicate superficial lesions with maximum sparing of adjacent tissue structures. However, in the purely incisional application mode pulsed mid-infrared lasers, though of potential usefulness in microsurgical indications (eg, surgery of the cornea), do not offer a suggestive alternative to simple scalpel surgery of the skin.

Effects of various laser types and beam transmission methods on female organ tissue in the pig: an in vitro study

The purpose of this in vitro study was to investigate and compare effects of various laser types (CO2, Argon, Erbium:YAG, Erbium:YSGG, and Holmium:YAG) and laser beam transmission methods (optical lens and flexible fiber) on ovarian and uterine tissue of the pig. The Erbium laser radiation was transmitted through Zirconium fluoride fibers (ZrF4). To circumvent the low mechanical stability of these fibers, we developed a special microlens system, which refocuses the radiation and protects the distal end from damage. Tissue lesions were performed with 1 and 5 joule. Histologic analysis of acute Er:YAG laser lesions reveal precise cutting effects with a minimal thermal damage zone of 40 microns and a high damage resistance of the fiber microlens systems. The extent of thermal damage caused by the Erbium:YSGG and CO2 laser is about two times larger, whereas the Argon and Holmium laser tissue lesions show a damage of the surrounding tissue of 200-300 microns. This study suggests that for precise cutting and coagulation, Erbium and Holmium lasers transmitted via our modified fiber tip may render the use of these lasers possible in a wide range of laparoscopic surgery applications.

Effect of the dynamic optical properties of water on midinfrared laser ablation

Water is a primary tissue chromophore in the midinfrared. Absorption of midinfrared radiation by water is a function of temperature and pressure, both of which rise rapidly during an ablative laser pulse. Data show that the absorption coefficient of water changes, by as much as two orders of magnitude, during a high-irradiance laser pulse. We present an ablation model that is fundamentally based upon Beer's Law but considers changes in the absorption coefficient. The model predicts that Er:YAG laser cuts will be deeper than Er:YSGG laser cuts; an opposite prediction would be made based upon the static, low-intensity absorption coefficient of water. The results of in vitro ablation of skin confirm that the dynamic optical properties of tissue need to be considered in the understanding of laser ablation as well as the design, manufacture, use, and regulation of clinical laser systems.

Rate process model for arterial tissue thermal damage: implications on vessel photocoagulation

A numerical model for thermal damage to human arterial tissue is presented, based on protein denaturation kinetics. The model involves determination of coefficients of rate processes A & delta E, which are tissue type-dependent (arterial tissue in this study), and definition of threshold damage. A feedback-controlled constant surface temperature device was used to induce 80 coagulative lesions of arterial human tissue ranging in temperature from 66 degrees C to 76 degrees C and in duration from 15 to 1,500 seconds. The measured coefficients were determined to be A = 5.6 x 10(63) s-1 and delta E = 430 KJ mole-1. These numerical values closely approximate the coefficients of the rate process for denaturation of collagen molecules. These and other histological observations strongly suggest collagen to be the primary coagulating component of arterial tissue at the onset of thermal coagulative damage. The ability of this model to predict onset of tissue coagulation during laser coagulation was studied using 10 postmortem human arterial samples exposed to argon laser irradiation.